Tony-B...
Posted: Sun Nov 08, 2009 3:18pm
Post Subject:
Battery charging
Dear Richard, without details about the domestic bank size, the panel output and if you have a charge controller or not it is difficult to give you a definitive answer. I will assume that your three domestic batteries equates to a bank of 330Ah and this means you can couple a solar panel of up to 30 watts directly to the bank without a regulator. Now, if the panel is a £20 Maplin special then it has a 1.5 Watt output. With the panel at 90 degrees to the sun it will produce about 0.1 (one tenth) of an amp. I doubt you will have it at 90 degrees to the sun and tracking it so in reality it will be far less than this. Lead acid batteries discharge at between 8% & 40% per month so lets say 20%. This means your domestic bank will discharge by 66Ah per month yet the solar panel will produce less than 24 Ah during a winter month with no clouds. Then you have to consider that you need to put back up to 40% more electricity than went out. based on these assumptions I would advise that you use the solar panel to charge the engine battery and make sure that when you are using the boat that you run the engine at charging speed for 5 hours or so. If you can easily take the batteries home for charging so much the better. This will go some way towards minimising sulphation and prolonging battery life. Please remember all this is based on assumptions about what you have. If I am wrong please come back with more information. Tony Brooks